Sheet feeding apparatus for a thermographic machine



March 1965 J. B. WARFIELD ETAL 3,171,960

SHEET FEEDING APPARATUS FOR A THERMOGRAPHIC MACHINE Filed Sept. 25, 1962 United States Patent 3,171,969 SHEET FEEDING APPARATUS FOR A THERMGGRAPHIQ MACHINE Joseph B. Wariield, Cincinnati, Uhio, and Daniel Smith, Riverdale, N.Y., assignors to Hnterchemical Corporation, New York, N.Y., a corporation of @hio Filed Sept. 25, 1962, Ser. No. 226,486 2 illaims. (Cl. 250-65) This invention relates to the reproduction of printed matter and other graphic materials. More particularly, it relates to the reproduction of said materials by a novel improved thermographic apparatus and method.

In recent years copying by thermography of typed or printed originals has become increasingly popular. The present therrnographic techniques involve placing the original in heat conductive relationship with a sheet of copy paper and then subjecting the original and copy sheet to intense irradiation. In such originals, the image and background areas are significantly diiferent in their ability to absorb high-intensity radiations particularly in the infrared region but also at other frequencies, with the resulting formation, when suitably irradiated, of a corresponding heat pattern which is then utilized to produce a visible image on a heat-sensitive copy sheet. In such a process it is apparent that the copy sheet must be constructed in such manner as to be capable of changing to a contrasting color in the areas which are heated. These thermographic processes and machines for carrying out the processes and certain types of heat-sensitive papers are described in numerous prior art patents, for instance, United States Patents 2,663,654-7; 2,710,263; 2,740,- 895-6.

The heat-induced image formation on the copy sheet may be caused by chemical reaction, usually to produce a dark colored image on a lighter background, or image formation may result from a physical change. In the latter type, the image formation may result from the transparentization of a fusible opaque coating or by transparentization of an opaque blushed lacquer coating to show a dark background or a background of contrasting color.

Using the techniques and apparatus presently known in the art as exemplified by the above mentioned patents, thermographic copying may be carried out by one of two methods: (1) back-printing, in which the graphic original, printed side up, is exposed to high-intensity radiation directly with the coated side of the heat-sensitive copying sheet immediately back of it; and (2) frontprinting in which the heat-sensitive copying sheet is placed on the original with its non-image forming side next to the original and then the original is exposed through the heat-sensitive copying sheet. When the back-printing technique is used, the heat-sensitive copying sheet need not be transparent to the high-intensity radiation. However, the graphic original sheet must be of minimal thickness in order that heat may be transmitted from the printed surface through the sheet to the copying sheet and must not contain any printed matter on the reverse side from that being copied. Because of these limitations, the back-printing technique is considered to be generally impractical and infrequently used.

The more extensively used existing technique is frontprinting. This technique requires a copying sheet which is transparent to the high-intensity radiation. While frontprinting thermographic copying is a very satisfactory method for making copies, it has certain aspects which are less than fully desirable. Because of the required radiation transparentness, it is necessary to use paper substrates in the copying sheet which are considerably more expensive and have less strength than avail- "ice able papers which are not transparent to the high-intensity radiation.

In addition, it is well known that the conventional infrared transparent copying sheets used in thermographic copying are not completely infrared transparent and do absorb and convert to heat a certain portion of the infrared rays. This in effect imposes a maximum limitation on the intensity of the infrared rays to which the copying sheet may be subjected. In other words, the intensity can not be so great that the portion absorbed by the copying sheet is sufiicient when converted into heat to produce a visual change in the background of the copying sheet.

We have now discovered a novel thermographic method and apparatus which overcomes the aforementioned deficiencies of both the front-printing and back-printing methods. In our novel method, there is no limitation to the thickness of the graphic original. Actually,

it may be on any substrate which is sufficiently flexible.

to pass through the thermographic copying apparatus, e.g., cardboard. It will be obvious to those skilled in the art, that, it necessary, the thermographic copying apparatus may be redesigned to accept even inflexible substrates.

Furthermore, the copying is unaffected by printing on the reverse side of the graphic original. In addition, the copying sheet need not be transparent and there is no problem of the copying sheet absorbing high-intensity radiation as the copying sheet is not exposed to such radiation. Therefore, there are substantially no limits to the intensity of the radiation.

Briefly stated, our invention involves intensely and uniformly irradiating the graphic representations on a graphic original with high-intensity radiation and then bringing the surface of a heat-sensitive copying sheet into contact with the irradiated surface of the graphic original. Since the temperature differential between the heated graphic representations and the background on the original will dissipate with the passage of time, the sooner the copying sheet is brought into contact with the exposed original, the better will be the results.

As best results are achieved by bringing the original into contact with the copying sheet immediately after exposure to the radiation, we have devised a novel thermographic copying apparatus for carrying out our novel method which provides for contacting the copying sheet with the original almost immediately after exposure of the original.

A preferred embodiment of our apparatus is shown in the accompanying drawing which is a diagrammatic side view of our apparatus. The driving mechanism for carrying the original and copying sheet through the apparatus is provided by four rollers: 1, 2, 3 and 4. These four rollers are drivingly engaged peripherally, an external driving force (not shown) being applied to any one of the rollers, preferably roller 2. The direction of rotation of the rollers is indicated by the arrows, rollers l and 4 rotating clockwise and rollers 2 and 3 rotating counterclockwise. The original 5, printed side 6 down, is fed into the nip between rollers l and 2 via feed guide '7 which may be an inclined plane such as an inclined tray. Rollers 1 and 2 drive original 5 through guide 8, along the path indicated by the arrows past infrared source 9 and into the nip between rollers 1 and 3. The original is exposed to intense infrared radiation as it passes highintensity radiation source 9 which may be a standard source of radiation high in infrared as described in the aforementioned patents e.g., Patent No. 2,740,895. Source 9 may suitably comprise incandescent filament It) in focusing reflector 11. In the nip between rollers 1 and 3, the exposed original comes into contact with copying sheet 12 which was fed into the nip between rollers 3 and 4 simultaneously with the feeding of original into the nip of rollers 1 and 2. Rollers 3 and 4 drive copying sheet 12 along a path defined by guide 13 into the nip of rollers 1 and 3 where said copying sheet is contacted with said graphic original. In order-that the driving force on original 5 and copy sheet 12 be continuous, it is preferable that the respective lengths of the paths defined by guides 8 and 13 be such that the leading ends of original 5 and copy sheet 12 reach the nip of rollers 1 and 3 before the back ends of said sheets are released from the hips of rollers 1 and 2 and rollers 3 and 4 respectively. Paths defined by guides 3 and 13 are preferably of such lengths that the leading ends of an original and of a copy sheet simultaneously inserted into this apparatus would reach the nip of rollers 1 and 3 at the same time. Since the rollers are drivingly engaged peripherally and consequent- 1y have the same peripheral speed, the copy sheet and the original will move through guides 8 and 13 at the same speed. Thus, the paths defined by guides 8 and 13 should be of the same length.

Where the copying sheet carries a heat-sensitive top coat'from which the image formed is read directly then the copy sheet is inserted into the apparatus face down so that the non-image forming surface of the sheetrcornes into contact with the exposed original. On' the other hand where the copying sheet is of the type where the image formed is read through the substrate which is various changes and modifications may be made therein 7 Without departing from the invention, and it is, therefore, aimed to cover all such changes and modifications as fall Within the true spirit and scope. of the invention.

We claim: 1. In a thermographic copying machine for the reproduction of a graphic original sheet in which the absorption of high-intensity infrared radiation difiers consider ably between graphic representations and a background,

the combination of sheet moving means comprising a first roller drivingly engaged peripherally with a second and with a third roller, power means for rotating one of said rollers, guidemeans for receiving a graphic original fed through the nip between said first and second rollers and guiding said graphic original into the nip between said first and third rollers, the path formed by said guide means being of'such a length that the graphic original will enter the nip between said first and third rollers prior to being completely released from the nip betwen said first and second rollers, means for intensely and uniformly irradiating said graphic representations with highintensity infrared radiation differentially absorbable in said graphic representations and said background positioned 7 along said path just prior to the end or" the path at the nip between the first and third rollers and means for feeding aheat-sensitive copying sheet into coincident contact With the irradiated surface of said graphic original through the nip between the first and third rollers.

2. The thermogr'aphic copying machine of claim 1, wherein said means for feeding said heat-sensitive copying sheet comprises a fourth roller drivingly engaged peripherally with said third roller and guide means for receiving a heat-sensitive copying sheet fed through the nip between said third and fourth rollers and guiding said copying sheet into the nip between said first and third rollers, the path formed by said copy sheet guide means being of such a length that a copying sheet will enter the nip between said first and third rollers prior to being completely released from the nip between said third and fourth rollers and that :1 copying sheet fed into the 'nip of the third and fourth rollers simultaneously with the feeding of a'graphic original into the nip of said first and second rollers will come into coincident contact with said graph original in the nip between said first and third rollers. V

References Cited in the file of this patent UNITED STATES PATENTS 

1. IN A THERMOGRAPHIC COPYING MACHINE FOR THE REPRODUCTION OF A GRAPHIC ORIGINAL SHEET IN WHICH THE ABSORPTION OF HIGH-INTENSITY INFARED RADIATION DIFFERS CONSIDERABLY BETWEEN GRAPHIC REPRESENTATIONS AND A BACKGROUND, THE COMBINATON OF SHEET MOVING MEANS COMPRISING A FIRST ROLLER DRIVINGLY ENGAGED PERIPHERALLY WITH A SECOND AND WITH A THIRD ROLLER, POWER MEANS FOR ROTATING ONE OF SAID ROLLERS, GUIDE MEANS FOR RECEIVING A GRAPHIC ORIGINAL FED THROUGH THE NIP BETWEEN SAID FIRST AND SECOND ROLLERS AND GUIDING SAID GRAPHIC ORIGINAL INTO THE NIP BETWEEN SAID FIRST AND THIRD ROLLERS, THE PATH FORMED BY SAID GUIDE MEANS BEING OF SUCH A LENGTH THAT THE GRAPHIC ORIGINAL WILL ENTER THE NIP BETWEEN SAID FIRST AND THIRD ROLLER PRIOR TO BEING COMPLETELY RELEASED FROM THE NIP BETWEEN SAID FIRST AND SECOND ROLLERS, MEANS FOR INTENSELY AND UNIFORMLY IRRADIATING SAID GRAPHIC REPRESENTATIONS WITH HIGHINTENSITY INFRARED RADIATION DIFFERENTIALLY ABSORBABLE IN SAID GRAPHIC REPRESENTATIONS AND SAID BACKGROUND POSITIONED ALONG SAID PATH JUST PRIOR TO THE END OF THE PATH OF THE NIP BETWEEN THE FIRST AND THIRD ROLLERS AND MEANS FOR FEEDING A HEAT-SENSITIVE COPYING SHEET INTO COINCIDENT CONTACT WITH THE IRRADIATED SURFACE OF SAID GRAPHIC CONTHROUGH THE NIP BETWEEN THE FIRST AND THIRD ROLLERS. 